Handbook of Turbomachinery Second Edition Revised - Ventech!

the main stream or into the preswirler (when ‘‘reversed’’ heat transfer is
simulated).
An important contribution to this subject, including the effect of
downstream blades on hot gas ingress, was made over the last few years by
the research team at Aachen University of Technology [135], providing
valuable experimental validation of numerical models that were generated
by the university.
Cooling Verification in an Engine Test
Traditional Instrumentation
Final validation of the selected cooling system is typically performed in a
prototype engine using detailed instrumentation with pressure and
temperature sensors in the cooled components of the hot section as well
as in the rotor–stator cavities supplying the cooling air. In the past,
instrumenting the airfoils with thermocouples in the full-scale turbine test
was the main technique for validating a design. The most expensive and
time-consuming factor was the instrumentation of the rotating components.
Furthermore, test data collection through a slip ring or telemetry system
provided only local temperature information. More recently, some new
techniques have been developed and implemented, which require much less
test preparation time and provide more detailed information about
component surface temperature distribution.
Borescope Port Inserted Pyrometer
This system is often based on a 908 side-viewing air-cooled pyrometer probe
that can be inserted radially through an existing borescope port. Air cooling
makes this system more convenient than nitrogen- or water-cooled
pyrometers. The optical head of the pyrometer is connected by a fiber
optic cable to a photodiode converter with outputs to an electronic
amplifier, a control and recording system, and a display system. The highspeed
recording system stores, displays, and plots the data identifying each
individual blade on the recording chart. The system is calibrated against
thermocouples installed in the blades and is qualified as a valuable
diagnostic tool to identify potential blade-cooling problems (cooling passage
blockage or restricted air entry orifice).
High-Temperature Thermal Paints
Another component temperature evaluation technique is based on the
application of high-temperature thermal paints, which permanently change
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